A - scrap the idea of a belt sander. You are almost certain to ruin the hand
rails with one. Nothing against you, it's just the nature of the beasts.
B- try a MEK stripper, it may work well and it is the least intrusive, at
least to the rails, method and won't harm them. Like chicken soup, it can't
hurt. It will however require the use of gloves, maybe a respirator, and a
well ventilated work area.
C- If it is oak, no matter what you do you had better plan on some sessions
with a stripper and a light wire brush so you can get all the stain and
finish out of the deep pores.
D - if you have to buy any sander make it a Random orbital sander with a
hook and loop sandpaper attachment arrangement.
E - if you are familiar with the care and feeding of card and or cabinet
scrapers they would be my tool of choice.
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